Recording and reproduction of sound



June 2s, 1.938, A, v ED' 2 ,122,193

RECORDING AND REPRODUCTION OF SOUND Filed Feb. 26, 1935 A 6 H n /0 I ATTORN EY Patented June 28, 1938 RECORDING AND REPRODUCTION OF SOUND Alda V. Bedford, Ccllingswood, N. J., assignor to Radio Corporation of of Delaware America, a corporation Application February 26, 1935, Serial No. 8,292

8 Claims.

This invention relates to means for limiting curvature in sound records of the groove type, and has for its principal object the provision of an apparatus and method of operation whereby the groove curvature of the record is prevented from exceeding the curvature of the reproducing stylus.

There is a well recognized limit to the higher frequency amplitudes that may be satisfactorily reproduced from a sound record of the groove type. Among the factors which determine this limit are a record groove curvature in excess of the reproducing stylus curvature and the pinch effect which results from narrowing of the groove at points where the record wave is large and is due to the use of a flat-faced record cutter. Both of these effects become increasingly worse at high frequencies and high amplitudes. Recording at high general level is desirable because it renders the record surface or background noise less conspicuous but has the disadvantage that very strong high frequency peaks are likely to be unreproducible. Such peaks had better not be recorded at full strength because they produce chattering which results in excessive record wear and in the production of undesirable scratching and rattling sound effects.

These difficulties may, of course, be avoided by the use of an over-loading or saturating amplifier which cuts off the peaks of both high and low frequency signals. This, however, is not satisfactory for the reason that the low frequency peaks can be reproduced and are required if wave-shape distortion and higher harmonics are to be minimized. In accordance with the present invention, this difficulty is avoided by l. segregating the high and low frequency components,

2. Passing the high frequencies through an amplifier adjusted to saturate and cut off excessive peaks,

3. Passing the low frequencies through an amplifier which does not out 01f the peaks and 4. Utilizing the combined outputs of the two amplifiers to actuate the record cutter.

Further objects of the invention are to provide an improved recording system which permits the extension of the recorded frequency range at the customary recording level, and to prevent the recording of high frequency levels which can not be reproduced due to the fact that the curvature of the record exceeds that of the stylus.

The invention will be better understood from the following description considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

The single figure of the drawing isa wiring diagram of a recording system made in accordance with the invention.

This recording system includes a sound pick-up device or microphone Ill from which acoustically modulated current is supplied to a cutter H through an amplifier A, a frequency selective network B, a high frequency amplifier C, a low frequency amplifier D, an output combining network E and an amplifier F interposed between the network E and the cutter ll.

Connected in the plate circuit'of the amplifier A is a resistor 12 of such value that the voltage V1 applied to the frequency selective network B is substantially constant with respect to frequency. The frequency selective network B includes capacity I3, resistance M, inductance l5, inductance l6, resistance H and capacity 58. These various elements are so arranged that most of the high frequency components are shunted to the amplifier C, most of the low frequency components are shunted to the amplifier D, and the sum of the voltages V2 and V3 equals the voltage V1.

Since amplifiers C and D have substantially the same effective amplification and their outputs are added in the output combining network E, the voltage V4 applied to the input circuit of amplifier F is proportional to the voltage V1.

The high frequency amplifier C, however, is made to have a characteristic such that it will amplify very high voltages much less than normal voltages, thus suppressing the peaks of the high frequency components at high amplitudes but leaving such components of lower amplitude unaffected. To this end, a bias potential source I9 is provided in the input circuit of amplifier C to ensure plate current cut-off on high negative swings of the grid potential, and a resistor 20 is connected in the output-circuit of amplifier C to reduce the plate current on high positive swings of the input potential.

cycles per second and the cutter ll cuts off at eight thousand cycles. This follows for the reason that cutting off excessively high amplitude frequencies of forty-one hundred to eight thousand cycles produces only harmonics of these frequencies, and these harmonics are of too high frequency to affect the cutter H. If the saturating amplifier C is made symmetrical in its action, only odd harmonics are generated so that the circuit may be made to out 01f excessive.

peaks down to about twenty-seven hundred cycles per second without serious disturbance from harmonics.

I claim:

1. An impulse recorder including means for separating the high frequency and low frequency components of the impulses to be recorded, means for suppressing only the high amplitude peaks of said high frequency components, and means for recombining said high and low frequency components.

2. An impulse recorder including means for suppressing only the high amplitude high frequency components of the impulses to be re corded and means for amplifying said impulses.

3. The method of restricting the curvature of a sound record which includes suppressing only the peaks of the high frequency components of high amplitude, and energizing a record cutter in accordance with said peak suppressed components.

4. A sound recorder including means for separating the high and low frequency components of the sound to be recorded, means for suppressing the high amplitude peaks of said high frequency components, and means for recombining said high and low frequency components.

5. A sound recorder including a frequency selective network for segregating the high frequency components of the sound to be recorded, and means including a saturation amplifier for suppressing only the high amplitude peaks of said components.

6. A sound recorder including a frequency selective network for segregating the high frequency components of the sound to be recorded, means including a saturation amplifier for suppressing only the high amplitude peaks of said components, means for amplifying the low frequency components of said sound, and means operable to recombine said high and low frequency components.

'7. A sound recorder including a frequency selective network for segregating the high frequency components of the sound to be recorded,

means including a saturation amplifier for suppressing only the high amplitude peaks of said ALDA V. BEDFORD. 

